Because of their energy and performance density, lithium ion batteries are popular energy stores particularly for uses in portable electronic devices. Lithium ion batteries comprise two electrodes which are spatially separated from one another by a separator whereby the lithium ions are reversibly intercalated or deintercalated into the electrodes. In particular, rechargeable lithium ion batteries (secondary batteries) or lithium ion storage batteries distinguish themselves by a high energy density, are thermally stable and are not subjected to a memory effect. Conventional lithium ion storage batteries use an anode made of carbon, usually graphite. The positive electrode usually has stable lithium transition compounds, for example lithium iron phosphate (LFP), lithium cobalt dioxide, lithium nickel dioxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. The charge transport takes place via an electrolyte, the electrolyte containing a lithium salt dissolved in a solvent. The prior art discloses different electrolytes and conductive salts. Frequently used conductive lithium salts are, for example, lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4) or lithium borate salts.
Good electrolytes distinguish themselves by a good heat stability and good SEI (Solid Electrolyte Interphase)-forming properties. The so-called Solid Electrolyte Interphase is formed during the first charging process as an interphase at the interface between the electrolyte and the electrode. On graphite anodes in this case, a reductive decomposition of the electrolyte takes place, and the reaction products of the electrolyte reduction can form an adhering and electronically insulating but lithium ion conducting film on the anode. The Solid Electrolyte Interphase then prevents the electrode materials from reacting chemically with the electrolytes and protects the electrolytes from further reductive decomposition and the anode from destruction by the solvent. Especially when graphite anodes are used, the formation of a dense and adhering film is needed for a reliable operation of a lithium ion battery.
Some electrolytes, however, frequently show disadvantages in terms of the formation of the Solid Electrolyte Interphase. Propylene carbonate, for example, forms no Solid Electrolyte Interphase. Without the formation of a Solid Electrolyte Interphase, however, a graphite anode is destroyed by cointercalation of the propylene carbonate.